Using whey as a fermentation medium presents the opportunity to create value-added products. Conditions were developed to partially hydrolyze whey proteins and then ferment partially hydrolyzed whey with Lactobacillus delbrueckii ssp. bulgaricus RR (RR; an EPS-producing bacterium). In preliminary experiments, pasteurized Cheddar cheese whey was treated with Flavourzyme to partially hydrolyze the protein (2 to 13% hydrolyzed). Fermentation (2 L, 38 degrees C, pH 5.0) with RR resulted in EPS levels ranging from 95 to 110 mg of EPS per liter of hydrolyzed whey. There were no significant differences in the amount of EPS produced during fermentations of whey hydrolyzed to varying degrees. Since a high level of hydrolysis was not necessary for increased EPS production, a low level of hydrolysis (2 to 4%) was selected for future work. In scale up experiments, whey was separated and pasteurized, then treated with Flavourzyme to hydrolyze 2 to 4% of the protein. Following protease inactivation, 60 L of partially hydrolyzed whey was fermented at 38 degrees C and pH 5.0. After fermentation, the broth was pasteurized, and bacterial cells were removed using a Sharples continuous centrifuge. The whey was then ultrafiltered and diafiltered to remove lactose and salts, freeze-dried, and milled to a powder. Unfermented hydrolyzed and unhydrolyzed whey controls were processed in the same manner. The EPS-WPC ingredients contained approximately 72% protein and 6% EPS, but they exhibited low protein solubility (65%, pH 7.0; 58%, pH 3.0).